As the hours went by I started to see more online posts like that -- runners in Boston and elsewhere making pledges to lace up their sneakers and hit the road. It felt like a groundswell of grass-roots action, a collective statement that this tragedy, no matter who perpetrated it or why, wasn't going to stop people from doing what they love.

The momentum has been building. As of early Tuesday afternoon, 360 people had logged more than 1,200 running miles on Obergefell's page.

People also have been sharing their stories with her.

"I ran to clear my head, but it didn't work. So I ran because I could. Because the freedom of running wasn't taken away from me. Because the running community stretches to all cities and all places, and I'm glad to be a part of it," one person wrote to Obergefell, a 26-year-old in Columbus, Ohio.

You don't have to pledge to run a marathon. Run a mile or a 5K -- or do a walk. The important thing is to get out there and get moving. Do it for Boston. Do it for your health. Or, if you use the simple app called Charity Miles, you can do it to raise money for one of the several worthy charities it features.

I'm doing it because I feel like I've got to do something. It's been 12 years since 9/11 and 18 years since the Oklahoma City bombing. I was safely miles away, in a middle school classroom, when a bomb exploded in downtown Oklahoma City, killing 168. But that morning is stuck in my memory forever. I'm running because I don't want any of these tragedies to change me or to change us as a people -- to make us afraid, to keep us indoors.

I am by no means a regular runner -- or even a runner at all. One of my friends saw a post about this idea on Facebook and thought I was joking. So please don't feel shy about signing up to do something new. I have no idea what I'm getting myself into -- and I think that's probably a good thing, at least for now.

CNN also hopes to make a video about the collective journey -- and I'm running to see what it will be like to (hopefully) complete this challenge as a group.

I could go on, but instead I'm going to go take a photo with my sneakers.